Just upgraded from 4.0.x to 4.6.1 and everything seemed to be working, until I clicked on a specific page type (Doctype) and I get this error???

I'm a little confused as its a very, very simple doctype... (See below)

Object reference not set to an instance of an object.Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace: 

[NullReferenceException: Object reference not set to an instance of an object.]
   umbraco.controls.ContentControl.addControlNew(Property p, TabPage tp, String Caption) +93
   umbraco.controls.ContentControl.CreateChildControls() +769
   System.Web.UI.Control.EnsureChildControls() +181
   umbraco.controls.ContentControl.OnInit(EventArgs e) +122
   System.Web.UI.Control.InitRecursive(Control namingContainer) +132
   System.Web.UI.Control.AddedControl(Control control, Int32 index) +276
   umbraco.cms.presentation.editContent.OnInit(EventArgs e) +1004
   System.Web.UI.Control.InitRecursive(Control namingContainer) +132
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1953

And this is all thats on the doc type

I can right click on the node and publish it and I can also save the doctype but I still get the following error? Anyone have any ideas?